Hearth structures for high temperature furnaces



E. PUGH July 9, 1957 HEARTH STRUCTURES FOR HIGH TEMPERATURE FURNACES Filed Jan. 8. 1954 United States Patent HEARTH STRUCTURES FOR HIGH TEMPERATURE FURNACES Emerson Pugh, Downers Grove, 11]., assignor to Western Electric Company, Incorporated, New York, N. 1 a corporation of New York Application January 8, 1954, Serial No. 403,001

1 Claim. (Cl. 26349) This invention relates to quickly replaceable hearth structures for high temperature furnaces.

The upper metal cap portion of the hearth structure of electric furnaces such as disclosed in Patent 2,556,962 is subjected to heat of approximately 2100 F. with the result that due to the oxidizing effect and mechanical stresses of the high temperature the metal cap deteriorates rapidly and the hearth structure has to be replaced frequently.

An object of the invention is to provide a furnace having an improved hearth structure capable of withstanding a relatively high temperature.

It is a further object of the invention to provide a quickly replaceable unitary hearth structure for a furnace, which may be readily moved into operative position and quickly removed therefrom. a A furnace illustrating certain features of the invention may have a fixed pedestal mounted on the floor, a hearth removably supported on the pedestal and including a plate and a slab of refractory material on the plate, an inverted cup-shaped hood removably supported on the plate and engageable with a sealing member thereon to form a closed inner chamber above said hearth in which parts are to be heated, a bell housing removably supported on the hood and engaging a sealing member thereon adjacent said hearth to form an outer chamber around the hood in which heating elements are mounted, and tubes on said plate passing through the slab and connectible to pipelines for flowing ga into and out of the inner chamber, said components being arranged so that the plate is insulated by the slab of refractory material from the intense heat of the inner chamber and so that when the bell and the hood have been removed, a defective hearth may be readily removed from the pedestal and a new hearth replaced thereon.

Other objects and advantages of the invention will become apparent by reference to the following detailed description and the accompanying drawings, illustrating a preferred embodiment thereof, in which:

Fig. 1 is a vertical central sectional view through the furnace; and

Fig. 2 is a vertical central sectional view of the unitary hearth structure.

Referring to the drawings the furnace comprises generally a unitary hearth structure 10, an inverted cupshaped metal hood 12 adapted to be lowered onto the hearth to form an inner chamber 14 in which the articles to be heated are placed, and an inverted cup-shaped bell 16 adapted to fit over and enclose the hood 12 and be supported on the lower portion thereof to form an outer chamber 17 enclosing the inner chamber 14. A plurality of electrical heating elements 18 are mounted on the inner walls of the bell 16 for heating the furnace and a plurality of pipes 19 and 20 pass through the walls of the bell to establish communication between the interior and exterior of the bell for supplying a predetermined atmosphere in the outer chamber 17. An inlet pipe 21 extends upwardly through the hearth 10 and is connected to a pipeline 22 through a union 23 for supplying a predetermined gas to the inner chamber and outlet pipe 25 extends through the hearth 10 and is connected to a pipeline 26 through a union 27 for exhausting the atmosphere therefrom. An additional pipe 28 extends through the hearth structure to provide an opening for the insertion of a thermocouple or other measuring instruments 29 into the inner chamber of the furnace. Each of the pipes 21, 25, and 28 is bonded to the plate 30 to provide a hermetic seal therebetween.

The hearth structure 10 comprises a circular metal plate 30 having a cylindrical skirt 31 depending from the outer edge thereof to form an extension thereof and from the lower end of the skirt extends a horizontal annular portion 32. An upwardly extending cylindrical flange 33 is formed on the outer edge of the portion 32 and 00- operates with an L-shaped portion 34 to form an annular channel for receiving a rubber sealing gasket 35.

A plurality of courses of fire brick or other refractory material is laid on the plate 30 around the pipes 21, 25, and 28 to form a layer or slab 40 of a predetermined thickness. The pipes 21, 25, and 28 are welded to the plate 30 to provide a hermetic seal therebetween. As shown herein the refractory slab 40 has sloping or conical walls 41. The unitary hearth structure 10 thus formed is supported in spaced relation to the floor 42 on a suitable pedestal 43 comprising a horizontal plate 44 supported on a plurality of legs 45, which in turn are supported on the floor 42. The plate 44 of the base is provided with clearance apertures for the pipes 21, 25, and 28. The unitary hearth structure as shown in Fig. 2 may be prefabricated and lowered onto the pedestal 43 and the pipes 21 and 25 connected to the pipe lines 22 and 26, respectively.

The hood 12 is adapted to be lowered onto the hearth 10 and has a flared or conical shaped wall portion 49 extending from the lower end of the cylindrical wall portion 50 thereof, which conical wall 49 conforms to the conical walls 41 of the slab 40. The hood 12 has a cylindrical skirt 51 projecting from the lower end of the conical portion 49 and the lower end of the skirt 51 is enlarged to form an annular bead 52 which is adapted to engage the rubber sealing gasket 35 and form a seal between the hood 12 and the plate 30 of the hearth structure 10. An annular shelf structure 53 extending outwardly from the cylindrical walls 51 of the hood 12 has a channel for receiving a rubber sealing gasket 54 and a conduit 55 through which coolant may be circulated to cool the gasket 54.

The bell 16 which is adapted to be raised from and lowered to an operative position as shown in Fig. 1 comprises relatively thick walls of refractory material 58 enclosed within a metal shell 59. An annular sealing ring 61 extends downwardly from the bell 16 and has a rounded bead on the lower edge thereof which may be hollow as indicated at 62 for the circulation of a cooling fluid therein, and which is engageable with the sealing gasket 54 on the hood 12 for effecting a seal between the hood 12 and the bell 16. The gasket 54 and the annular shelf structure 53 also serve to support the bell 16. Thus, when the hood 12 and the bell 16 are lowered onto the hearth It] the components cooperate with each other to form a sealed inner chamber 14 within the hood 12 and a sealed outer chamber 16 surrounding the inner chamber 14 so that the atmosphere in the inner chamber may be purged therefrom and hydrogen flowed therein and the atmosphere in the outer chamber may be purged therefrom and an inert gas supplied thereto as described in more detail in the above-referred-to patent.

The articles to be heat treated maybe placed upon the upper surface of the slab 411) but preferably are placed on a perforated metal tray 67 provided with feet 68 which rest on the upper surface of the slab. The relatively thick refractory slab 40 of the hearth structure serves to insulate the plate 30 and the seal 35 from the intense heat of the furnace which rises to a temperature of from 2000 to 2200 F. so that the plate 30 during the operation of the furnace is heated only to a temperature of from 200 to 300 F. With this design of hearth structure only the slab 40 of refractory material is exposed to the high temperatures while the plate 30 is relatively cool and free from oxidation and thus the hearth structure does not deteriorate rapidly with use but has a relatively long life. However, when the refractory slab 4t) deteriorates through repeated heating and cooling stresses, it is a relatively simple matter, after the bell 16 and the hood 12 have been removed, to disconnect the pipes 21 and 25 from the lines 22 and 26 and raise the unitary hearth structure from the pedestal and remove it, and then place another prefabricated unitary hearth structure on the pedestal. The removal of an old hearth structure and the replacement thereof with a new hearth structure requires about half an hour and thus it does not necessitate an extended shutdown of the furnace and does not appreciably interfere with the continued operation thereof.

It is to be understood that the above-described arrangements are simply illustrative of the application of the prinicples of this invention. Numerous other arrangements may be readily devised by those skilled in the art which will embody the principles of the invention and fall within the spirit and scope thereof.

What is claimed is:

A base for a high temperature furnace having a removable domed hood, which comprises a stationary platform having a horizontal supporting member and a plurality of depending legs in engagement with a floor, a

unitary hearth structure supported removably on said platform above and in spaced relation to the floor, said hearth structure comprising a metal plate supported removably on and positioned immediately adjacent to the horizontal supporting member of the platform, said metal plate having a marginal portion for supporting the domed hood to form a gas-tight chamber for heating articles therein, a layer of refractory material supported upon the metal plate, said layer forming a bottom for the gas tight chamber and insulating the metal plate and stationary supporting member from direct exposure to heat within the chamber, and vertical tubes extending through and attached fixedly to the metal plate with upper portions of said tubes extending through the layer of refractory material to the top surface thereof and lower portions of said tubes depending below the supporting member of the stationary platform through complementary oversized openings formed in the supporting member, the lower ends of said tubes being detachably arranged to conduct gases into and out of said chamber, and an article supporting tray mounted upon the upper surface of the layer of the refractory material.

References Cited in the file of this patent UNITED STATES PATENTS 1,234,789 Morris July 31, 1917 1,569,444 Wirz Jan. 12, 1926 1,977,399 Northrup Oct. 16, 1934 2,006,685 Moore July 2, 1935 2,137,869 Woodson Nov. 22, 1938 2,178,527 Wellman Oct. 31, 1939 2,215,322 Germany Sept. 17, 1940 2,245,647 Burby et a1. June 17, 1941 2,545,877 Descarsin Mar. 20, 1951 2,556,962 Field June 12, 1951 

